It worked like a charm, thanks! Values lower than 90 seem to work fine, but going over 120 just breaks FOV; instead of becoming wider it becomes way narrower (tried it with 132). So yeah, if anyone with an ultrawide monitor is reading this, just follow this guide and the poor ultrawide implementation will be fixed.
Here is what I'm rocking and I can confirm in works flawlessly: https://www.mouse-sensitivity.com/?share=53659ce78fcf91cb8519ce068ee73e12